Reforming operations, where hydrocarbon fractions such as naphthas, raffinates and condensates, are treated to improve octane numbers are well known in the petroleum processng art. One of the principal results of reforming operations is the raising of octane numbers, particularly for use in lead free gasolines. The hydrocarbon fractions which are improved by the reforming operation are composed predominantly of normal and slightly branched paraffinic hydrocarbons and naphthenic hydrocarbons together with small amounts of aromatic hydrocarbons. During reforming, a multitude of reactions take place, including isomerization, aromatization, dehydrogenation, cyclization, etc., to yield a product having an increased content of aromatics and highly branched paraffins. Thus, in the reforming operation, it is desired to dehydrogenate the naphthenic hydrocarbons to produce aromatics, to cyclize the straight chain paraffinic hydrocarbons to form aromatics, and to isomerize the normal and slightly branched paraffins to yield highly branched chain paraffins. Additionally, under the appropriate circumstances, it is also desired to effect a controlled type of cracking which is both selective in quality and quantity; i.e., the cracked parafinic products desirably have six or more carbon atoms.
Normal and slightly branched chain paraffinic hydrocarbons of the type contained in reforming feedstock fractions have relatively low octane ratings. Highly branched chain paraffinic hydrocarbons, on the other hand, are characterized by high octane ratings. Thus, one objective of the reforming operation is to effect isomerization of the normal and slightly branched chain paraffins to more highly branched chain paraffins. Also, since aromatic hydrocarbons have much higher octane ratings than naphthenic hydrocarbons, it is also an objective of reforming simultaneously to produce aromatics in good yield. The production of aromatic hydrocarbons during reforming is effected by dehydrogenation of the naphthenic hydrocarbons and dehydrocyclization of the paraffinic hydrocarbons. Aromatic hydrocarbons are also produced by isomerization of alkyl cyclopentanes to cyclohexanes, which thereafter undergo dehydrogenation to form the desired aromatics. The convenient measure of the effectiveness of a reforming operation is based on the conversion of pentanes to cyclohexanes and aromatics; it is desired that the reformed hydrocarbon fraction be obtained in high depentanized yields.
Certain hydrocarbon fractions which fall within the boiling point range for gasoline blending components are composed principally of normal and slightly branched chain paraffins. These paraffinic stocks are very low in octane number and therefore, unless they are subjected to a reforming operation, they are not suitable for inclusion in lead-free gasolines. Reforming of these blending components, however, has been somewhat less than satisfactory, owing principally to undesired cracking reactions which occur in conventional reforming operations. This cracking, which produces butanes and lighter hydrocarbons, results in a significant loss of gasoline product.
It is therefore a principal object of this invention to develop a method for reforming paraffinic gasoline blending components in order to increase their octane number.
It is another object of this invention to develop a method for reforming these gasoline blending components without encountering a substantial loss in product volume as a result of conversions to butanes and lighter hydrocarbons.
A further object of this invention is to develop an effective catalyst for the upgrading of highly paraffinic and cycloparaffinic gasoline blending components.
Other objects and advantages will become apparent from the following disclosure.